The present invention relates to a hollow, structure of very large cross-section, for example larger than 100 m.sup.2, and consisting of tubular sections placed end to end along a lengthwise axis.
Structures of this kind are typically large cross-section conduits, for example larger than the conventional industrial fabrications of about 2 m.sup.2, which may or may not be buried, for carrying water or other fluids, pressurized or otherwise, or even for cable ducts, but the invention relates particularly to the production of very large cross-section enclosed structures, even larger than 100 m.sup.2, which can be used, for example, for pedestrian or vehicle passageways or for parking. The invention is also applicable to relatively short, covered structures, for use as cellars, silos or bomb shelters or the like.
Furthermore, the invention relates to non-enclosed structures usable, for example, for realizing irrigation canals.
The most commonly used technique comprises the use of tubular sections of circular cross-section, which are assembled end to end of various methods. This technique has drawbacks which increase with the diameter of the conduit, even if the lengths of the sections are shortened, namely: manufacture, transportation, handling and installation. In any event, setting aside the problems of manufacture, problems of sheer size arise once an external diameter of 2.5 m is attained, which corresponds to the normal limit for road transportation. When very large quantities of fluid are to be carried, a plurality of parallel conduits must be provided, which is a costly solution, or the conduit may have to be manufactured at the construction site, using masonry construction techniques or the work may need to be carried out in underground shafts, which is also costly and time-consuming in manufacture or construction.
Furthermore, as is known, conduits of circular section are the most suitable for high internal pressures. A cross-section of this kind is the easiest to produce when sections corresponding to the whole cross-section or contour of the conduit are manufactured. On the other hand, a circular cross-section of this kind has disadvantages for other uses. A conduit of circular cross-section gives rise to stresses in the supporting ground which have a pronounced maximum in the median region. Consequently, if the soil is loose, considerable differential subsidence may occur after the conduit is laid. Circular cross-sections are poorly suited to effective use of restricted space in an urban environment. Lastly, the weight of the conduit is comparatively high; in the case of modular sections covering the entire cross-section or contour, the constituent material is, in fact, uniformly distributed along the entire periphery, whereas the stresses are not thus distributed.
To overcome these various problems, it has been proposed--see, for example, German Pat. No. 2,157,191--to construct conduits having cross-sections which are flattened at their base, by assembling prefabricated longitudinal components on site, each corresponding to a part of the contour or cross-section of the conduit and made of corrugated sheet metal. Such structural components have a low mechanical strength in respect of external forces, so that there is no certainty that the contour and the leakproof sealing will be maintained. Furthermore, the corrugations increase flow resistance.
French Pat. No. 733,098 and U.S. Pat. No. 2,400,071 disclose techniques consisting in assembling a large number of small components, each having a transverse flange for joining onto adjacent components. The large number of components means that they have to have identical configurations, which results in a cross-section of circular contour being adopted, and, in this case, stress resistance requires the junctions to alternate in the lengthwise direction. U.S. Pat. No. 2,400,071 provides for taking into account the stresses exerted on the conduit wall and for using for the upper part of a tunnel components which are of lower strength than those for the lower part. However, an assembly of alternating joints of components of different characteristics is of uncertain strength and, in addition, introduces a further complication in the assembly of a great number of small components, which is difficult to perform satisfactorily using unskilled manpower.
It is thus apparent that there is an unsatisfied need for tubular hollow structures with a flattened base, of high mechanical strength, and whose manufacturing, transportation and installation costs are considerably lower when compared with current techniques.